This invention relates to disk drives that store and retrieve information on a spinning, rigid magnetic recording disk.
Conventional hard disk drive systems spin at least one disk containing a thin magnetic media layer or layers in which a head of the system stores data for later retrieval. The head includes an inductive transducer which converts electrical signals from read/write electronics, usually associated with a computer, to magnetic fields which in turn create magnetic patterns in the media during information storage. During reading the transducer converts those magnetic patterns to electrical signals. Alternatively, the written signals may be read with a magnetoresistive sensor included in the head, which senses a change in current or voltage due to the effect of the magnetic patterns on the resistance of the sensor.
The head also includes an aerodynamic slider which is designed to interact with an air layer that accompanies the moving disk to cause a slight separation of the disk and the head, the essentially stationary head xe2x80x9cflyingxe2x80x9d over the spinning disk. Though this separation serves the purpose of avoiding wear of the head and the disk, it also reduces resolution of signal communication between the transducer and the media. To increase data storage density, the air separation between the transducer and the media has generally decreased over many years of development in the magnetic storage industry. However, a smaller separation generally increases the probability of impact between the head and the disk during operation of the disk drive system, often resulting in destruction of the disk drive and loss of stored information. Perhaps the most destructive type of impact can occur due to dynamic instabilities of the head, which cause a corner of the head to impact the disk, focusing the energy transfer of the impact in the relatively small region of contact between the corner and the disk.
Instead of completely separating from the disk, U.S. Pat. No. 4,901,185, to Kubo et al. discloses a slider designed to operate with a leading edge lifted by the air layer that accompanies the spinning disk while a trailing edge contacts the disk, the slider holding a magnetic read/write transducer that is designed for vertically magnetized recording. To avoid destructive wear and to minimize variations in the head-disk separation the head is mounted on the trailing edge of the tail dragging slider so that a constant separation between the head and the disk is maintained.
In U.S. Pat. No. 4,819,091, Brezoczky et al. propose a magnetic recording head comprised of a slider composed of a single crystal material, onto which a magnetic read/write transducer is appended. During operation of the disk drive system the rubbing between the disk and the slider produces an electrical attractive force maintaining contact between the slider and the disk. To avoid destructive wear of the head it is important that the slider be so much more thermally conductive than the much larger disk that the slider is maintained at a lower temperature than the disk during operation of the system. It is also important for the Brezoczky invention to maintain an orientation of the slider relative to the spinning disk that avoids flying and other problems.
An object of the present invention was to provide a hard disk drive recording system which affords substantially continuous operational contact between the head and disk without damaging the head or the disk. More specific objects included the intuitively contradictory goals of minimizing dynamic instabilities of the transducer that would otherwise cause damage or interfere with the reading and writing of data, providing flexibility for transducer conformance to the rapidly spinning, rigid disk surface and providing rapid accessibility of the transducer to various points on the disk surface for data storage and retrieval.
The above objects have been achieved in a hard disk drive system employing an elongated flexible beam to hold a transducer in sliding contact with a hard magnetic disk during writing and reading, the flexure beam extending lengthwise over the disk substantially along the direction that the transducer slides on the disk. This orientation aligns the most rigid dimension of the beam with the direction of relative motion during contact between the disk and the transducer, thereby reducing deleterious vibrations that may otherwise be induced by friction between the disk and transducer. Due to the alignment between the rapidly spinning disk and the direction of the beam most resistant to mechanical forces, the flexure and transducer can be made smaller and lighter.
The flexure size reduction affords increased flexibility in a direction normal to the disk surface, while the weight reduction provides lower inertial resistance to disk surface variations, both of which help to decrease wear and avoid catastrophic impacts between the head and the disk. The decreased mass and increased flexibility also allow for a reduction in the load applied to hold the transducer to the disk, which along with the decreased mass and increased flexibility affords a reduction in area of contact between the transducer and the disk without a destructive increase in pressure therebetween, while a smaller area of contact reduces the aerodynamic lift of the transducer from the disk, affording a further reduction in applied load. The small transducer contact area also minimizes frictional forces that cause vibrations and power loss, the reduction of friction also allowing a skew to occur between the flexure axis and the motion of the disk at the contact area without inducing excessive lateral vibrations. A magnetic poletip or pair of magnetic poletips separated by an amagnetic gap borders the disk in the contact area of the transducer, reducing spacing between the transducer and the information storage medium of the disk.
The disk can be rotated with the flexure beam oriented along the direction of sliding in either a forward or a reverse mode. In the forward mode a localized portion of the disk contacting the transducer moves generally from an end of the beam adjacent to the actuator to an end of the beam adjacent to the transducer, while in the reverse mode such a portion of the disk moves generally from the transducer end to the mounting end of the beam. One difference between spinning the disk in these two modes is the amount of vertical force between the transducer and the disk due to the friction between the transducer and the disk, as translated by the moment arm of the flexure beam. Spinning the disk in the reverse mode generally creates additional loading between the transducer and the disk, as the beam is usually mounted in a plane outside the disk surfaces, allowing a lower static load to be applied to the beam, although this force is minimized by the extremely low beam angle and flexibility. The ability to operate in either the forward or reverse mode has an added benefit during start up of the system, when bi-directional motion may be employed during motor seeking and for loosening the slider from the disk, an operation which commonly causes conventional aerodynamic sliders, which are not designed for sliding in either direction, to dig into the disk.
In a preferred embodiment a gimbal is interposed between the slider and the flexure beam, providing the slider with additional flexibility to react to disk surface anomalies by pitching and rolling. This improved conformance between the disk and the slider decreases wear to the head and the disk in addition to increasing the tendency of the transducer to remain in contact with the disk. A microscopic slider having three hard disk-contacting projections or pads, at least one of which contains a pole structure of the transducer, is attached to the gimbal. Having a pole structure encased in a disk-contacting pad offers a durable reduction in spacing between the pole structure and the media, while the pads hold the body of the slider sufficiently away from disk to avoid air bearing effects caused by the thin air layer that travels with the disk. The gimbaled, three pad structure can maintain stable contact with the rapidly spinning disk despite disk surface anomalies or differences in pad height.
Design of the suspension beam and gimbal for reduced vibration has been realized to be essential to the operation of the system, as the forcing function from friction between the contact slider and the disk is larger than the drag typically encountered by a flying slider of the prior art, while the mass is less. In particular, the suspension must avoid geometries in which resonant frequencies may be positively coupled to changing frictional forces. Moreover, resonant modes of vibration, which theoretically comprise an infinite series, including lateral, longitudinal, and torsional modes which may intercouple, must not interact with a forcing function such as friction so that a negative effective spring constant occurs, or positive feedback can result in a untenable vibration. Due to other beam requirements, such as providing low-capacitance conductive leads and an effective mass and vertical load force several times less that of conventional sliders, discovery of these rules of low-vibration contact slider suspension design does not lead to trivial solutions.
In minimizing vibration of the three pad, gimbal combination, it has been found to be important to have the resultant force from friction directed away from, rather than toward, any gimbal pivot axis about which that force acts as a torque. Since the gimbal preferably has such a pivot axis located between the leading and trailing pads, this suggests that the friction force on the leading pad or pads should be less than that on the trailing pad or pads. With the disk spinning in the forward mode and all three pads sliding on the disk, it is thus preferable for reduced vibration to have one leading pad and two trailing pads, such that the two trailing pads are located furthest from the mounting end of the beam. To increase transducer accessibility to the outer tracks of the disk surface in this case, the magnetically active pole structure may be located in the outside trailing pad. For this, both of the trailing pads may be formed with magnetically active pole structures and associated transducers, which are then tested before beam attachment to determine which pad has the better transducer in order to sort the chips for operation on either up or down sides of the disk. On the other hand, for forward mode spinning with a single magnetically active trailing pad and a pair of leading pads, it is important that the leading pads have reduced friction, which may be accomplished in those pads due to reduced relative size, lower load, employment of low-friction leading pad materials, at least partial levitation of the leading pads or some combination of these techniques. The goal of having a resultant frictional force that trails the gimbal pivot axis is realized in the reverse spinning mode by essentially reversing the orientation of the contact pads compared to that of the forward mode, so that a single leading and a pair of trailing pads again results.
An adapter may be provided which fits the beam to a compact, lightweight rotary actuator for accessing various tracks of the disk. The adapter offers a preselected angular shift from the bearing of the actuator arm, which pivots in a plane generally parallel to the disk surface, to that of the flexure beam, which approaches the disk surface at an oblique angle. The angle at which the flexure beam approaches the disk is chosen so that the beam is bowed slightly, providing a force or load holding the transducer to the disk without the stress and inaccuracy that result from forming an angle in the beam. The adapter contains a shock absorbing structure extending adjacent to the flexure beam on an opposite side from the disk, so that shocks which propel the transducer from the disk surface are transferred to the adapter rather than retained by the beam, allowing the transducer to return to the disk surface with greatly reduced force. The beam is designed to provide a similar shock absorption function by overlapping the chip, so that shocks which lift a pad or pads of the gimbaled chip are limited by the chip impacting the beam, which absorbs energy from the chip and thereby mitigates damage upon recontact of the pad or pads with the disk. This close separation of the chip and the beam also protects the thin gimbal members from overstress.
In either the gimbaled or non-gimbaled embodiment, the head is designed to avoid flying, a dramatic departure from conventional design, the lack of airlift allowing a lower loading force to be applied to maintain contact between the head and disk. The lower load also allows the head and flexure to be lighter and more flexible, which further reduces wear and impact problems. In sum, the flexure beam orientation and non-flying head allow the employment of the lightweight head and flexure combination, which in turn affords long-term, non-catastrophic, virtually continuously sliding operation.